Two-Codebook CSI Reporting With Basis Subset Feedback Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing CSI reporting schemes in wireless communications, such as those in the 5G NR system, suffer from high feedback overhead due to the increased number of subbands, particularly in Type-II CSI reporting, which is not efficiently managed by current 3GPP Rel.-15 specifications.
Innovation Solution
A two-codebook CSI reporting scheme is introduced, utilizing a first codebook for spatial beam components and a second codebook for delay components, allowing for a common delay domain basis subset to reduce feedback overhead by reporting a reduced set of delay domain indicators and combining coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Type-II CSI reporting with subband-based W2 precoding is used, then channel state information accuracy is improved, but feedback overhead increases significantly
Solution Approach 1:
The feedback is segmented into two parts: W1 (wideband spatial precoder) and W2 (subband combining coefficients). The W2 matrix is further segmented by selecting only the B strongest columns corresponding to dominant channel paths, reducing the number of coefficients that need to be reported while maintaining accuracy for the most significant channel components.
Solution Approach 2:
The patent extracts and reports only the most significant components of the channel state information. Specifically, it identifies and reports the B strongest combining coefficients in W2 that correspond to the dominant channel paths, while omitting weaker coefficients. This selective extraction reduces feedback overhead while preserving the essential channel characteristics needed for accurate precoding.
2Measurement precision
If the number of subbands increases, then frequency selectivity of CSI reporting is improved, but feedback overhead increases linearly
Solution Approach 1:
Instead of reporting all W2 coefficients for all subbands, the patent applies partial action by reporting only the B strongest coefficients per subband. This partial reporting approach provides sufficient frequency-selective precoding information without the linear overhead increase that would result from reporting all coefficients, achieving a practical balance between accuracy and overhead.
3Productivity
If comprehensive CSI reporting framework is implemented, then MIMO transmission performance is improved, but system complexity increases
Solution Approach 1:
The comprehensive CSI reporting framework is segmented into manageable components: W1 for wideband spatial precoding and W2 for subband combining. This segmentation allows the system to implement sophisticated MIMO transmission with high performance while reducing computational complexity by processing and reporting each component separately rather than handling the complete precoding matrix as a single complex operation.
Data Source
AI summary
The present disclosure relates to methods and apparatuses (UE, network node or gNB) for CSI reporting. The method performed by a UE comprises: receiving from the gNB, a radio signal via a MIMO channel, wherein the radio signal contains at least one DL-RS according to a DL-RS configuration; estimating said MIMO channel based on said received at least one DL reference signal for configured subbands; calculating a precoder matrix or a CSI matrix for a number of antenna ports of the gNB and configured subbands; the precoder matrix based on a first codebook and on a second codebook and a set of combining coefficients for complex scaling/combining one or more of vectors selected from the first codebook and the second codebook; and reporting, to the gNB, a CSI feedback report and/or a PMI/RI, used to indicate the precoder matrix or the CSI matrix for the configured antenna ports and subbands.